How We Should Interview

The Evolution of the Technical Interview

Ignorance played a crucial part in me getting an internship offer at Microsoft 36 years ago. I had no idea what Microsoft's interview process was like. There was no internet full of cautionary tales or sample interview questions. I prepared the same way I had prepared for every other interview up until that point. I read all the information they mailed me ahead of the interview and took notes of the relevant questions I had from that reading. I was ready for all the standard questions: "Why did you choose Computer Science?" "Why do you like programming?" "Tell me about a challenge you faced and how you overcame it." "Where do you see yourself in five years?" But within fifteen minutes of being on Microsoft campus, I became keenly aware that this was going to be a very different experience.

My day began with my Julie, my recruiter. She told me I was going to be meeting with several engineers from different product teams throughout the day. Then Julie closed her introduction with a key line, "Today you're going to be presented with all sorts of different technical problems. Just stay relaxed and remember to think out loud." She wished me luck and then sent me on my way. I got in my rental car to drive across campus to my first interview in building 15. In that short drive I was thinking, "What kinds of technical problems? Why do I need to relax?"

My first interviewer greeted me in the lobby of and we took a one minute walk down the hall, during which all standard pleasantries were exchanged. We reached a conference room and walked inside. He asked me to have a seat. Then he handed me a pad of paper and a pencil and said, "You're standing on the face of the earth. You walk a mile due south, then a mile due east, and then a mile due north and you end up in exactly the same place. Where are you?"

I said, "I've heard this before. It's the polar bear / penguin question. You're a polar bear at the north pole. A penguin at the south pole can't walk any further south."

He responded. "Right. Where else?" I grinned, realizing that the fun was now beginning.

"North pole is one. Can't be the south pole. How about the equator?" I drew an equator line on the paper and then drew a slightly slanted line down, then a flat line across, and then a slightly slanted line up. I looked at the resulting trapezoid and say, "Nope, equator doesn't work."

The interviewer encouraged me, "Great, you've knocked out the obvious cases. Keep going."

I drew a circle to represent the globe, then drew the polar bear's path at the top of the circle: a curved line down the side of the circle, a curved line across the circle, and a curved line up the other side of the circle. I drew a curved line across the center of the circle and put an X across it. I added an X at the bottom of the circle. Now I had a visual to work with. "Where else?" I thought out loud. In the middle of the northern hemisphere, I drew another triad of curved lines, down, across, up, and reasoned about the resulting shape. "Once you're south of the north pole, anywhere in the northern hemisphere is going to have you ending on the same latitude that you started, but in a different spot on that latitude."

Then I turned my attention to the southern hemisphere, where I drew yet another triad. "The same looks true for the southern hemisphere." I stared at the page for a minute, then said, "Well, the south pole was never an option because you can't walk a mile due south from the south pole. What if we start a mile north of the south pole?" I drew a line down the bottom part of one side of the circle. "Hmmm, no, because you can't walk east from the south pole." I studied my drawing a bit more, then said, "aha." I drew a curved line across the bottom of the circle, saying, "The latitude that is a mile north of the latitude where the circumference of the globe is one mile. You walk a mile south from anywhere on that upper latitude, and then you'll walk east right back to where you just were. Then your walk a mile north will land you back in the same spot on that upper latitude." I drew what essentially looked like a lasso on the paper. One line down and a circle around the globe. "So an infinite number of spots, from anywhere on that latitude." I looked at my paper again and added my conclusion, "Very neat. Had never thought about that before."

Without a pause, the interviewer said, "Very good. Where else?" I wasn't exactly shocked, but his comment had me thinking (this time just to myself), "No way … there's more? More than infinity?" I then said out loud, "The only two shapes that work are the triangle at the north pole and this lasso in the southern hemisphere." I took another short look at my paper and said, "Aha, it's an infinite number of latitudes in the southern hemisphere, all below that first latitude ring. A mile above 1/2 mile circumference. A mile above 1/3 mile circumference. 1/4 mile. etc." I then thought of the more generalizing statement, "A mile above any latitude where walking a mile east will result in you returning to the same place."

The interviewer said, "Nice work."

I smiled and said, "That's interesting."

The smile was short lived as the interviewer immediately asked, "Pick any procedure you want and explain it to me."

Me: "Okay; driving a car from point A to point B."
Interviewer: "Okay. Go."
Me: "First, you get in the driver's seat."
Interviewer: "Where is that?"
Ah ha, this is going to be fun.
Me: "A car has four wheels and one or more doors. You can identify the front of the car by two or more clear glass lamps, which are called headlights. If you see red glass lamps, you're at the back of the car. Standing in front of the car and looking at these headlights, walk around the car to your right and open the first door. This is the driver's door."
Interviewer: "How do I open it?"

And so it continued.

My brain was now awake. And my technical communication was now warmed up. That was the first 30 minutes of my day of technical interviewing. And I now understood what Julie had been telling me.